The invention relates to a method for determining the concentration of aerosols in hot gases, particularly in exhaust gases of internal combustion engines, the removal of volatile and semi-volatile particles by heating the exhaust gas, as well as measuring of the concentration of the aerosols, optionally in a partial flow of an optionally diluted exhaust gas flow, as well as a device for executing the method, comprising a subsystem for removing volatile and semi-volatile particles by heating the exhaust gas, as well as a measurement system for measuring the concentration of the aerosols, optionally with a device for dividing a partial flow of the exhaust gas flow into the measurement system, as well as, optionally, a system for diluting the exhaust gas flow.
In order to determine the aerosol concentration in the exhaust gas of internal combustion engines, as well as for testing and research purposes and for checking for legal specifications, certain process sequences are necessary in order to provide accurate information. Basic process sequences have even found their way into legislation.
Typically, a hot dilution is performed in which volatile and semi-volatile particles are removed in a heated pipe with wall temperatures between 300 and 400° C. This system is referred to as a “Volatile Particle Remover (VPR).” The concentration of the aerosols is then determined using a particle counter whose inlet temperature should be no greater than 35° C.
Depending on the displacement and/or output of the internal combustion engine, the “volatile particle remover” draws its samples from a full or partial flow dilution system. For research purposes, a sample is often also drawn directly from the exhaust system.
The drawback of all of these systems is their high energy consumption, for which reason they are not well suited to on-board measurement systems. What is more, such systems require an external pressurized air supply; they work with high sample flow rates, which is problematic especially for partial flow dilution systems, and the flow rates in the system overall are very high, which further contributes to the high energy consumption.
It was therefore the object of the present invention to provide an improved method and a device suited to same which avoids the abovementioned drawbacks and enables precise measurements of the aerosol concentration in the exhaust gas of internal combustion engines with low energy consumption.
To achieve this object, the method described at the outset is characterized in that, in a first stage, the exhaust gas is divided into two partial flows, both of which are heated, with one of the partial flows being filtered at least once, preferably before heating; that the two partial flows are subsequently recombined; that, in a second stage, the exhaust gas is again divided into two partial flows, with one of the partial flows being heated even further than in the first stage, and with the other partial flow being filtered at least once; and that the two partial flows are subsequently recombined, and the concentration measurement is performed on the total flow.
According to a first advantageous embodiment, a provision is made that both partial flows are heated to at least 150° C. in the first stage.
Advantageously, the unfiltered partial flow is heated to at least 300° C. in the second stage.
Another, optional feature of the invention is that the unheated partial flow is cooled before the first filtering in the second stage.
According to another embodiment of the invention, a provision is made that the unheated partial flow is cooled to a temperature that does not exceed a temperature of 35° C. after recombination of the partial flows.
Preferably, a provision can also be made that throughput measurements are performed in the unfiltered partial flow, and preferably in the combined total flow as well.
To achieve the abovementioned object, the device described at the outset is characterized by a first branching piece for dividing the exhaust gas into two partial flows, heating devices for both partial flows, and at least one filter device in one of the partial flows, preferably before the heating device; furthermore by a combining piece in which the two partial flows are brought together; furthermore by a second branching piece arranged downstream from the combining piece for dividing again into two partial flows, with another heating device being provided for one of the partial flows and at least one additional filter device being provided in the unheated partial flow; and furthermore by a second combining piece before the measurement system, in which combining piece the two partial flows are subsequently recombined.
According to an advantageous embodiment of this device, a cooling device is arranged after the first combining piece and before the or before each filter device.
Another advantageous embodiment of the device is characterized by throughput measurement devices between at least one branching piece and the following combining piece, each in the unfiltered partial flow.
In such a device, an additional throughput measurement device can also advantageously be present between the last combining piece and the measurement system.